People watch a television news report, showing file footage of North Korean leader Kim Jong-Un, at a railway station in Seoul on September 9, 2016.<br />North Korea claimed September 9 it has successfully tested a nuclear warhead that could be mounted on a missile, drawing condemnation from the South over the “maniacal recklessness” of young ruler Kim Jong-Un. / AFP PHOTO / JUNG YEON-JE

US President Barack Obama, warning of “serious consequences”, called the leaders of South Korea and Japan for consultations, a White House spokesman said Friday, after Pyongyang said it conducted its fifth nuclear test.

“The president indicated he would continue to consult our allies and partners in the days ahead to ensure provocative actions from North Korea are met with serious consequences,” White House press secretary Josh Earnest said.

North Korea declared it had conducted a “successful” fifth nuclear test, which South Korea described as the largest explosion of its kind by Pyongyang.

The White House stopped short of calling it a nuclear test, referring to “reported seismic activity” near a known North Korean nuclear test site.

Obama was briefed on the situation as he flew home from a trip to Asia aboard Air Force One, Earnest said.

He said Obama, who arrived in Washington shortly after midnight Thursday, also consulted with South Korean President Park Geun-hye and Japan’s Prime Minister Shinzo Abe in separate phone calls from the presidential aircraft.

“The president reiterated the unbreakable US commitment to the security of our allies in Asia and around the world,” Earnest said.